This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. This study will test whether serial magnetic imaging(MRI), positron emission tomography(PET), other biological markers, and clinical and neuropsychological assessment can be combined to measure the progression of mild cognitive impairment(MCI) and early alzheimer's disease(AD). The information obtained by studying changes in the brain images of MCI and AD patients and healthy individuals, as well as other assessement tools, will be used to determine the best methods for measuring treatment effects in patients MCI and AD. Aproximately 800 participants, ranging in age 55 to 90, will be recruited for the study: 400 patients with MCI, 200 with early AD, and 200 normal controls. Patients with MCI and normal controls will be followed for 3 years, and those with AD will be followed for 2 years. At 6-month intervals all participants will be seen in person or contacted at the time of each scan. All participant will undergo repeated scanning and blood and urine biomarkers will be collected at the time of each scan. All patients will be asked if they are willing to undergo lumbar puncture at baseline and year one, with the goal of a minimum of 20% and as many as 50% of each group providing CSF samples for analysis and storage for future analyses.